Decorative surface covering and process therefor



June 1962 R. w. CHARLTON ET AL 3,040,210

DECORATIVE SURFACE COVERING AND PROCESS THEREFOR Filed Jan. 5, 1957 quuqu INVENTORS. RALPH W. CHARLTON ROCCO J SERGI ATTORNEY Uite States This invention relates to surface coverings having resinous binders and particularly to linoleum having a controlled electrical resistance for use in hospitals, arsenals, and the like.

It is well known that if two surfaces of insulating materials are rubbed together and separated following contact, an electrostatic charge will be built up between the two surfaces. This accumulation of electrostatic charge under these conditions can readily be observed when one walks across a woolen carpet in a dry atmosphere and then touches an object which is grounded. It is apparent that the building up of such charges on objects and the subsequent discharge with the formation of a spark can be particularly hazardous in areas which contain combustible or explosive compositions, such as in arsenals and explosives manufacturing plants, and also where combustible chemicals exist in admixture with air or oxygen such as in chemical plants and hospital operating rooms.

The problem in hospital operating rooms is particularly serious and has received a great deal of attention in the past. Certain anesthetic gases such as cyclopropane, ethyl ether and ethylene can form violently explosive mixtures with air or oxygen. Fatal accidents, which have been attributed to ignition of these mixtures as a result of an electrostatic spark discharge, have occurred. For this reason, the National Board of Fire Underwriters has set forth rules governing safe practice for hospital operating rooms. One of the principal series of rules relates to the type of flooring which should be used in such locations. The code calls for the use of conductive flooring which must have a resistance of between 25,000 and 1,000,000 ohms as measured between two electrodes placed three feet apart on the floor.

The above requirements set forth both a lower limit and an upper limit for resistance. The need for an upper limit is obvious, since this requirement assures that static charges will be conducted away and dissipated. The requirement for a lower limit is of equal importance. If the floor were constructed of aluminum or iron, or other low-resistance material, there would be a great hazard to personnel from electric shocks from the electric equipment within the room.

Resilient floorings such as linoleum, rubber, and the like can be rendered electrically conductive in a manner to pass the above-mentioned standards by blending an electrically conductive material such as graphite with the binder used in formulating the product. These products are satisfactory from the standpoint of safety but have an aesthetic disadvantage in that they are black in color.

Decorative efiects can be obtained in conductive flooring materials in several Ways. The addition of carbon black or graphite to cement terrazzo floors produces a product which can pass the National Fire Protection Association code. However, floors of this type are hard and contribute markedly to fatigue for people who must stand on them for long periods of time. Also, the conductive matrix is generally softer and less durable than the decorative marble chips and thus tends to wear at a greater rate. After a period of time there can be poor contact of shoes of personnel with the conductive areas of the floor. In addition, with a flooring of this type there is a problem in meeting an additional requirement of the National Fire Protection Association code which states that no point on a non-conductive element in the surface of the floor shall be more than A inch from a conductive element.

Resilient decorative flooring having a terrazzo-like appearance has been made using a vinyl resin composition. This product is made by consolidating a layer of mixed conductive and non-conductive granules upon a layer of conductive granules in a press. The conductivity of a product prepared in this way depends on the presence of a progressively increasing concentration of conductive elements as one moves from the top surface to the bottom surface of the product. This varying concentration means that as the product wears, the decoration will tend to change and the proportion of black conductive elements in the surface will increase over a period of time. Consequently, the appearance of areas of the floor which are subjected to high wear will tend to be diiferent from the appearance of other areas of the floor. Not only will the proportion of black areas in the floor tend to increase during wear but also the resistance of the floor will decrease during wear, necessitating costly replacement if the resistance falls below the standard. The method of producing this product by consolidating mixed granules in a press is expensive both in terms of materials, since costly vinyl resins are used, and in terms of labor, since separate batches of composition must be added in controlled amounts to the press on each pressing cycle. In

addition, the product is available only in the form of tiles,

and thus, during installation an elaborate grid may berequired to insure that a continuous electrical path is present within the finished installation.

It is an object of the invention to provide a resilient flooring having a controlled electrical resistance which has a pleasing and an attractive appearance. A further ob ject of the invention is to provide a resilient decorative flooring with a controlled electrical resistance which is available in sheet form. Another object of the invention is to provide a decorative resilient flooring characterized by stability of resistance and uniformity of decoration during wear. Other objects and the advantages of the invention will appear hereinafter.

In accordance with the invention, a decorative resilient surface covering having a controlled electrical resistance is produced by consolidating and pressing multicolored chips containing conductive areas into a sheet and thereafter laminating said sheet to a conductive base.

The invention will be described with reference to the drawing which is a schematic representation of a method of prepming a decorative linoleum product in accordance with the invention.

Pieces 11 of conductive linoleum composition are delivered from a hopper 12 onto an endless conveyor 17 which passes over and around wheels 18, 19. Pieces 13, 15 of conventional, non-conductive linoleum composition in contrasting colors are delivered to the conveyor from hoppers l4, 16. The mixed pieces 20 are sheeted between conventional calender rolls 21, 22 to form a heavily striated sheet 23. The striated sheet passes to a cutter 24 from which chips of a controlled size 25 fall onto a second endless conveyor 26. The controlled size chips pass from the second conveyor onto an inclined chute 2.7 and are fed with the depth controlled by an adjustable bafiie 7.8 to calender rolls 29, 30. A decorative sheet 31 is produced which is laminated to a conductive backing comprising a conductive linoleum sheet 33 upon a fabric back 34. The lamination is carried out between press rolls 36 to produce the product 37, which passes to a conventional stoving operation.

The surface of the calender, roll 30' is maintained in a clean, film-free condition by being continuously contacted with a fabric sheet which is delivered to cleaning bath 39 from roll 33. The fabric sheet 40, wet with solvent, contacts the surface of calender roll 36, thereby removing any adhering linoleum composition. The sheet with adhering linoleum composition is taken up on roll 41.

Linoleum composition useful in preparing products in accordance with the preferred embodiment of the invention are formulated according to conventional practices of the linoleum industry. The compositions in general comprise a blend of linoleum binder, pigments and fillers. Linoleum binder is an oxidized mixture of drying oils and resinous material. Drying oils and semi-drying oils such as linseed oil, soybean oil and in general any oil which upon oxidation yields a substantial amount of the oxidized glycerides of linoleic acid and linolenic acid are satisfactory. In preparing the linoleum binder, the drying oils are blended with resinous material such as rosin, ester gum, coumarone-indene resin, synthetic resins of phenol formaldehyde type and the like. Normally, the linoleum binder contains from about to about 35 percent resinous material. The resinous material is added to the drying oils either before, during or after oxidation which is normally carried out at a temperature between 120 F. and 240 F. for from 8 to hours.

Although linoleum binder is preferred in manufacturing surface coverings in accordance with the invention, numerous resinous substances can be used in formulating useful binders. Such thermoplastic and elastomeric resins as butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, natural rubber, polymerized chloroprene, polymerized vinyl chloride, vinyl chloride-vinyl acetate copolymer, polymerized vinylidene chloride, copolymers of the above with each other and with other monomers copolyrnerizable therewith, mixtures of the above with each other and the like can be used in formulating resinous binders for use in the invention. in some cases, the resin can be blended with compatible plasticizers such as tricresyl phosphate, dioctyl phthalate, dipropylene glycol dibenzoate and the like in formulating the binder.

The binder is mixed with pigments and fillers in accordance with conventional practice in the surface covering industry. Normally a blend of vegetable fillers, such as cork, wood flour and the like, and mineral fillers, such as whiting, clay and asbestos, in conjunction with suitable pigments are used. The finished composition normally contains from about 15 to about 50 percent binder and about 85 to about 50 percent pigments and fillers.

In accordance with the invention, a conductive composition is prepared from conventional ingredients by adding during formulation electrically conductive materials. Conductive carbon is the preferred conductive ingredient and is added in an amount of from 10 percent to about percent by weight of the composition. It has been found that from 15 percent to 25 percent conductive carbon is a particularly effective range in formulating a preferred conductive linoleum composition in accordance with thhe invention. The conductive composition, after being thoroughly mixed, is extruded and cut or otherwise formed into pieces which are mixed with similarly formed pieces of conventional non-conductive composition in contrasting colors. As many separate batches of nonconductive composition can be made up as there are colors in the finished product. For example, if a simple black and White product is desired, only one non-conductive batch with White pigmentation need be made for blending with the black conductive composition. If, however, a more complex decorative effect is desired, separate batches of many colors may be made up for mixing with the conductive composition.

The conductive and non-conductive composition in the form of pieces, chips, granules and the like are passed to conventional calender rolls or otherwise sheeted. In accordance with the invention, the conductive composition comprises from about 10 to about percent of the mixture. The sheet produced is a heavily striated decorative sheet which shows all the colors which were used to formulate the original composition and contains from about 1 percent to about 14 percent and preferably 1.5 percent to 10 percent carbon.

This sheet is passed to conventional cutting or dicing equipment in which it is comminuted into uniform chips. These chips should have faces between about inch in width and no more than about /2 inch in length. Thus, faces from as small as inch square to as large as /2 inch square are useful. it has been found that rectangular chips having faces with widths greater than /8 inch and lengths less than inch are particularly effective, t t is, chips from Ms inch square to "7 inch square. T he iess of the chips is the same as the thickness of the heavily striated decorative sheet and normally is from 1 to 4 times the thickness of the finished deco "ative sheet. A thickness between 0.10 and 0.16 inch is particularly effective.

in producing a decorative conductive linoleum sheet in accordance with the preferred embodiment of the invention, the chips are fed to calender rolls wit-h the depth adjusted to be from about 10 to about 30 times the thickness of the finished decorative sheet. At least one roll of the calender is cleaned in accordance with US. Patent 2,624,068, issued on January 6, 1953, to Joseph F. Dobry. The continuous cleaning of at least one calender roll serves to remove any adherent linoleum composition from the roll, whereby the roll continuously presents a clean, film-free surface to the composition being calendered. Therefore, a minimum of distortion, stretch or elongation of the chips takes place. They are compressed and compacted as they pass through the nip be veen the calender rolls and become bonded into a smooth unitary sheet without being distorted or elongated so as to lose their identity and general form. in this way, no point in a non-conductive element in the surface of the sheet is more than A inch from a conductive element, and the sheet has a plurality of conductive paths from top to bottom.

Although calendering is the preferred method of sheet formation when a decorative conductive linoleum sheet is produced in accordance with the invention, the chips can be deposited on a base and then consolidated by use of a flat bed press. This method is not an unbroken continuous operation as in calendcring and thus tends to be more costly. When a decorative conductive sheet in accordance with the invention is produced using resinous compositions other than linoleum, sheet formation can be by calendering or pressing. The process must be carried out in such a way that in the product, no nonconductive element in the surface be more than inch from a conductive element.

The decorative sheet poduced is laminated to a backing sheet which has a controlled electrical resistance. This backing sheet is conventionally a conductive resinous composition sheet which can be bonded to a fabric or burlap backing for added strength. This conductive back is formulated from a mixture of resinous binder, pigments and fillers and contains from about 10 percent to about 35 percent conductive carbon. In the production of a decorative conductive linoleum sheet in accordance with the invention, a decorative sheet produced as described above is laminated to a conductive plain linoleum back which preferably contains from 15 percent to 25 percent carbon. This conductive back is bonded to a fabric or burlap sheet in order that the finished product have sufficient strength to withstand the strains encountered during subsequent stoving of the product. After the lamination, the product is cured or stoved by being maintained at a temperature of about F. to F. for from about 3 to about 8 weeks.

In some cases where increased resistance stability of the product is desired, the fabric or burlap sheet can itself be rendered electrically conductive by dipping the burlap sheet in a dispersion of conductive carbon, thereby yielding, after drying, a burlap with conductive particles imbedded and held within the fibers. In addition, where Example The following linoleum compositions were prepared by blending linoleum binder (75 percent linseed oil plus 26 percent rosin,- oxidized and partially gelled) with pigments and fillers in the proportions indicated.

Composition Number I II Color Conductive Composition (pounds):

Linoleum Binder; Wood Flour Carbon Other Pigments and Fillers. Total Each composition was individually mixed and extruded in inch diameter shapes (known in the linoleum industry as doggies). The doggies were blended to form a uniform heterogeneous mass which was formed into a primary striated sheet with a thickness of 0.130 inch.

The sheet was cut into chips having a thickness of 0.130 inch and face dimensions of inch square. These chips were fed in a bank 1 inch deep to a calender, the top roll of which was continuously cleaned by contact with a kerosene soaked cloth which served to remove any adherent linoleum cement. A decorative sheet 0.075 inch in thickness was produced having sharply defined areas in black, light green and white, a pleasing pattern.

A base sheet of thickness of 0.055 inch was prepared by calendering the following composition onto a sheet of burlap.

Composition IV Color Black Conductive Yes Composition (pounds):

Linoleum binder 310 Wood flour 200 Carbon 150 Other pigments and fillers 24 Total 684 The base was laminated to the decorative sheet so that the surface in contact with the cleaned roll was exposed. Asa result of slight compaction in the lamination step, a finished product thickness of 0.125 inch was obtained.

The product was stoved by being held at 165 F. for 5 weeks. After stoving, the resistance was determined in accordance with the procedure outlined in section 6-2 of pamphlet NBFU No. 56, entitled Recommended Safe Practice of the National Board of Fire Underwriters for Hospital Operating Rooms, published in June 1954. In this test, a suitably calibrated ohmmeter with an open circuit potential of 500 volts D0. and a short circuit current of 2.5 to 10 milliarnperes is used. Each electrode weighs 5 pounds and has a flat, dry, circular contact area 2 /2 inches in diameter which comprises a surface of aluminum or tin foil 0.005 to 0.001 inch thick backed by a layer of rubber inch thick and measuring 50 plus or minus 10 hardness as determined with a Shore type A durometer. In making the test, the electrodes are placed 3 feet apart on the sheet. The measured resistance in accordance with this test procedure was 47,000 ohms, thus falling Within the prescribed limits set forth by the National Board of Fire Underwriters. Also, in the exposed surface of the product, no conductive element was more than A inch removed from another conductive element.

The decorative conductive surface covering product prepared in accordance with the invention is characterized by possessing a controlled electrical resistance determined by the relative quantities of conductive carbon in the decorative and base layers. The product has a pleasing decoration which remains substantially constant throughout wear through the decorative layer. This is brought about by the uniform carbon content throughout the decorative layer which also contributes to a constancy of resistance during wear. The product passes the stringent code of the National Board of Fire Underwriters in that no non-conductive element is more than inch -removed from a conductive element. sheet form, for example, in the case of linoleum 6 feet wide by up to feet long. Thus an installation can be made with an absolute minimum of dirt-collecting seams which is of particular importance in hospital op erating room installations. The virtual absence of seams means that conductivity throughout theinsta-llation can be effected without the use of an elaborate grid system over the surface to which the product is bonded.

Any departure from the above description which conforms to the present invention is intended to be included within the scope of the claims.

We claim:

1. A smooth static-conductive resilient surface covering having a random decorative surface with conductive areas and non-conductive areas wherein all points on the non-conductive areas are within /1 inch of a conductive area which comprises a calendered linoleum composition upper sheet of uniform thickness having said random decorative surface comprising a uniform mixture of about 10 to about 40 percent of conductive linoleum composition granules and about 60 to about 90 percent of non-conductive linoleum composition granules, securely bonded to a smooth resilient linoleum conductive backing sheet, each of said conductive granules in the surface of said decorative sheet being electrically interconnected with said backing sheet and a non-conductive sheet bonded to the back of said backing sheet, the ratio of conductive areas to non-conductive areas being uniform throughout the thickness of said upper decorative sheet.

2. A smooth static-conductive resilient surface covering having a random decorative surface with conductive areas and non-conductive areas wherein all points on the nonconductive areas are within 4 inch of a conductive area which comprises a calendered linoleum composition upper sheet of uniform thickness having said random decorative surface comprising a uniform mixture of about 10 to about 40 percent of conductive linoleum composition granules containing about 15 to about 25 percent by weight of conductive carbon and about 60 to about 90 percent of non-conductive linoleum composition granules, securely bonded to a smooth resilient linoleum conductive backing sheet containing about 10 to about 35 percent by weight of conductive carbon, each of said conductive granules in the surface of said decorative sheet being electrically interconnected with said backing sheet and a non-conductive sheet bonded to the back of said backing sheet, the ratio of conductive areas to non-conductive areas being uniform throughout the thickness of said upper decorative sheet.

3. A method of producing a decorative surface covering in sheet form having a controlled electrical resistance as measured between two points on the wearing surface thereof and being operative for dissipating static elec- It is available intricity which comprises forming a heavily striated first sheet from a discrete uniform mixture of about 10% to about 40% resinous composition rendered electrically conductive by the presence of about 10% to about 35% conductive carbon and about 90% to about 60% non conductive linoleum composition, cutting said first sheet into uniform chips, feeding said chips to the nip between a pair of calender rolls having clean surfaces thereby forming a smooth unitary decorative layer of uniform thickness throughout which has a plurality of conductive paths completely through the thickness thereof and which presents a plurality of conductive and non-conductive areas, every point of said non-conductive areas being less than one-quarter inch from a conductive area, laminating said decorative layer to a linoleum backing of uniform thickness rendered uniformly electrically conductive throughout by the presence of about 15% to about 25% conductive carbon and laminating to the opposite surface of said backing a non-conductive fibrous sheet.

4. A method of producing a decorative inoleum sheet having a controlled electrical resistance as measured between two points on the wearing surface thereof and being operative for dissipating static electricity which comprises forming a heavily striated first sheet from a discrete uniform mixture of about 10 percent to about 40 vpercent linoleum composition rendered electrically conto the nip between a pair of calender rolls, the surface of said rolls presenting a clean film-free surface to the chips, thereby forming a smooth unitary decorative layer of uniform thickness throughout which has a plurality of conductive paths completely through the thickness thereof and which presents a plurality of conductive and nonconductive areas, every point on said non-conductive areas being less than A inch from a conductive area, and laminating said decorative layer to a conductive backing of uniform thickness throughout in such a way that the surface of said decorative layer in contact with the clean calender roll is exposed, said conductive backing being a linoleum layer rendered electrically conductive by the presence of 15 percent to 25 percent conductive carbon uniformly distributed therein bonded to a fabric backing.

5. The method according to claim 4 wherein said chips have face areas between /s inch square and inch square and a thickness between 1 and 4 times the spacing of said calender rolls.

References Cited in the file of this patent UNITED STATES PATENTS 2,341,360 Bulgin Feb. 8, 1944 2,457,299 Biemesderfer Dec. 28, 1948 2,473,183 Watson June 14, 1949 2,624,668 Dobry Jan. 6, 1953 2,694,831. Benedict et al Nov. 23, 1954 2,729,770 Robbins Jan. 3, 1956 2,786,161 Lunden Mar. 19, 1957 

